1. Field of the Invention
This invention principally relates to the field of lifting and pulling devices and, more particularly, to such devices which develop force multiplication through the manual operation of a lever member.
2. Description of the Prior Art
Various pulley and rope systems are known as simple machines for developing a mechanical advantage, i.e. the ratio of the force exerted by the machine to the force exerted on the machine, which is greater than one. A simple block and tackle is a common example of such a machine. One set of pulleys is fixed in position and another set of pulleys is attached to the weight to be lifted. Each movable pulley is suspended by two "falls" of rope. By increasing the number of pulleys and falls of rope, the mechanical advantage is increased according to the formula: W = nP, where W is the load, P is the force applied, and n is the number of falls of rope that support the moving block. Another way of putting it is that the block and tackle develops the mechanical advantage of two for each movable pulley. One disadvantage of such a machine is the requirement for the additional rope needed to develop the loops about the extra pulley pairs. Furthermore, the mechanical advantage is limited by the number of pulleys and falls of rope in a given block and tackle system in accordance with the above-stated formula. If additional mechanical advantage is needed, additional operative pulleys must be incorporated into the system.
Other simple machines have incorporated levers and variable grip mechanisms for developing the desired mechanical advantage in lifting, hoisting ahd hauling various loads. Such machines are limited in the mechanical advantage achieved to the well-known relationship of the relative distances from fulcrum to load and fulcrum to point of force application.
Related prior art of which applicant is aware include the following U.S. Pat. Nos.: 224,746 of Trump; 430,282 of Gauttard; 434,701 of Conway; 520,426 of Hammerly; 535,884 of Bellamy; and 2,107,500 of Price et al. Except for the Price et al., all of the patents listed were issued before 1900. It is therefore apparent that very little development of an innovative nature has occurred in this century in the field to which the present invention relates. This suggests the possibility that the present invention constitutes an entirely new type of simple machine, despite its apparent simplicity and the fact that its outstanding mechanical advantage is developed through the adaptation of a principle usually taught in high school physics courses.